Using Transition-Metal Complexes as Catalysts for Radical Addition

Laboratory Experiment Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

pubs.acs.org/jchemeduc

Using Transition-Metal Complexes as Catalysts for Radical Addition Reactions: A Laboratory Experiment Demonstrating the Important Role of Catalysts in an Organic Transformation Reaction Journi E. Burke,† Emily A. Khoury,† Grant J. Koskay,† Christopher J. LeWarne,† Emily A. Reeson,† Katherine L. Sandquist,† Kayode D. Oshin,*,† and Matthias Zeller‡ †

Department of Chemistry, Creighton University, Omaha, Nebraska 68102, United States Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States

‡

J. Chem. Educ. Downloaded from pubs.acs.org by VITERBO UNIV on 05/09/19. For personal use only.

S Supporting Information *

ABSTRACT: This laboratory experiment demonstrates the important utility of transition-metal complexes as catalysts in the addition reaction of carbon tetrabromide (CBr4) to select alkenes. This application offers students the opportunity to understand why transition-metal complexes are worth synthesizing. The experiment builds on fundamental theories presented during first-year general chemistry courses and integrates concepts taught in organic chemistry, inorganic chemistry, organometallics, and instrumental analysis. It incorporates some advanced laboratory practices for students to assimilate with, such as literature searches and interpretation; organometallic compound analysis; catalysis experiment design; reaction mechanisms; NMR spectroscopy with comprehensive spectra interpretation; and X-ray crystallography. KEYWORDS: Upper-Division Undergraduate, Organic Chemistry, Inorganic Chemistry, Organometallics, Laboratory Instruction, Hands-On Learning/Manipulatives, Addition Reactions, Catalysis, NMR Spectroscopy

■

INTRODUCTION

ATRA is a noteworthy reaction for undergraduate students to explore because it is one of the most atom economical methods available to functionalize alkenes efficiently and form new carbon−carbon bonds, which are notoriously difficult to make.4−6 Most organic chemistry courses dedicate an entire chapter to alkene addition reactions; therefore, this experiment can be used to reinforce the concepts and theories presented in those lectures. First reported by Kharasch et al. in the 1940s,7 ATRA can proceed in the presence of free-radical precursors and has been efficiently catalyzed by transition-metal complexes incorporating nickel,8 ruthenium,9 iron,10 and copper.11 The reaction has evolved to include important hybrids such as atom transfer radical polymerization (ATRP),12,13 and atom transfer radical cyclization (ATRC).14,15 Two review articles and one laboratory experiment solely focused on ATRP have been published in this Journal,16−18 but there are no articles available on ATRA reactions. Therefore, this paper offers a new laboratory module for instructors to consider adopting in their courses. This experiment was developed to complement a preliminary synthesis and characterization module performed by students, and it provided them with a chemically relevant process to apply the compounds made in that module.19 Pedagogically, it provided students with an opportunity to answer an important question they naturally ask after any synthesis and character-

One important recommendation for chemical educators following the 2010 ACS DivCHED conference is to expose more undergraduate students learning about organic synthesis to catalytic approaches from a theoretical and practical perspective.1 This viewpoint is part of a concerted effort to educate the next generation of STEM students in green and sustainable practices.2 In 2013, seven guiding papers from that conference were published in this Journal.1 Of relevance to this article is the paper by Dicks and Batey highlighting their development of an undergraduate catalytic chemistry course.3 They described chemical catalysis as an important focal point for chemistry students and a foundational pillar of green chemistry that continues to revolutionize organic chemistry.3 Developing laboratory experiments that showcase the importance and application of chemical catalysis supports the ACS DivCHED’s goal of educating the next generation of students. Herein, an integrated laboratory experiment is presented highlighting the application of transition-metal compounds as catalysts in an organic transformation reaction known as atom transfer radical addition (ATRA). It builds on fundamental theories presented in first-year general chemistry courses, with respect to the role catalysts play in chemical kinetics and equilibrium, and provides an opportunity for instructors to integrate concepts also taught in organic chemistry, inorganic chemistry, and instrumental analysis. This integrated approach to solve scientific problems reflects modern research practices offering students a valuable laboratory experience. © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: September 4, 2018 Revised: April 25, 2019

A

DOI: 10.1021/acs.jchemed.8b00721 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

Laboratory Experiment

homolytic cleavage of an alkyl halide (R−X) by the catalyst in its lower oxidation state, generating a halide radical (X•) and organic radical (R•). The halide radical adds to the metal center of the catalyst resulting in a one-electron oxidation, and there is an anti-Markovnikoff addition of the organic radical to the alkene making a new alkyl radical. This alkyl radical abstracts the halide (X) from the catalyst, effectively returning it back to its original oxidation state via a one-electron reduction. This process closes the catalytic cycle and forms the desired monoadduct. On the basis of literature recommendations,21 the primary transition metal used by students in this experiment was copper, which exhibits an oxidation change between (+1) and (+2) states. The (+1) oxidation state is air-sensitive, so reactions were set up with copper complexes in the air-stable (+2) oxidation state. To facilitate a reduction of the (+2) state to the (+1) state, which initializes the ATRA reaction, students used a reducing agent. Ascorbic acid was chosen because it is inexpensive, relatively safe to handle, and reported to be very effective.22 In addition, because ATRA reactions involve radical−radical coupling processes, reducing agents also serve an important role in preventing irreversible radical termination reactions from occurring due to the persistent radical effect phenomenon.22

ization experiment: What meaningful way can I utilize the compound I just made? What chemical process can be improved using my compound? The second pedagogical goal was for students to observe and appreciate the important role catalysts play in organic transformation reactions. The final pedagogical goal was for students to comprehend the importance of integrating concepts and techniques from different subdivisions of chemistry to achieve a desired result. The experiment was incorporated and tested in the undergraduate chemistry curriculum for four years and performed by 26 students at the second-year and upper-division undergraduate levels. It was offered in an advanced integrated laboratory course, enrolling an average of eight students per term, and a second-year undergraduate introduction to undergraduate research course enrolling an average of five students per term.

■

EXPERIMENT

Laboratory Schedule

After completion of the preliminary synthesis and characterization module,19 this catalysis experiment was broken up into four laboratory sessions and performed over a two-week period meeting twice a week for 4 h blocks. Students were grouped into small teams of 3 or 4. The first laboratory meeting was a lecture to discuss ATRA reactions. Before attending this session, each group was asked to bring one or two articles that provided some background and experimental information on ATRA to share with the class. One relevant paper for instructors to consider using is written by Taylor et al.20 Students used the second laboratory period to set up their ATRA reactions, the third period to process and analyze their reactions, and the final period to discuss their results with the class. Next, they were all tasked with writing formal laboratory reports and/or organizing group oral presentations to communicate their findings.

Reaction Components

All reactions performed by students required the following six contributing parts further discussed below: (1) Alkene (2) Alkyl halide (3) Catalyst (4) Reducing agent (5) Reaction solvent (6) Internal standard Alkene. This was the compound to functionalize and transform into a monoadduct. Students used five alkenes providing three different structural motifs to investigate (Figure 2). • Straight-chain alkenes: 1-hexene, 1-octene, 1-decene • Aromatic alkene: styrene • Organic ester: methyl acrylate There are several varieties of olefins commercially available for instructors to consider using, with over 380 varieties offered through Sigma-Aldrich alone.23 Alkyl Halide. This substrate is the source of halide that adds to the alkene during the reaction. The more halides there are present on the substrate, the easier it will be to functionalize the alkene as there are more R−X bonds that can be cleaved to form a radical.24 Therefore, reactivity is expected to decrease as follows: RX4 > RHX3 > RH2X2 > RH3X. To ensure the addition of alkyl halide substrate to alkene in all reactions, students used carbon tetrabromide (CBr4) as the halide source. Catalyst. This is the most important component of the reaction with respect to the objective of this experiment. Students were able to observe that, without a catalyst, ATRA reactions did not occur, or occurred to a smaller extent because

Reaction Mechanism

Presently, transition-metal catalysts are used to facilitate ATRA reactions and employ a mechanism that involves free-radical intermediates as shown in Figure 1.21 It begins with the

Figure 1. Proposed ATRA reaction mechanism employing a copperbased catalyst and ascorbic acid as the reducing agent.

Figure 2. Alkene substrates used. (A) Straight-chain: 1-hexene, 1-octane, 1-decene. (B) Aromatic: styrene. (C) Organic ester: methyl acrylate. B




Figure 3. Complexes tested as catalysts: (A) [Ni(TPMA)(Br2)], (B) [Co(TPMA)(Br)][Br], (C) [Cu(TPMA)(Br)][Br], (D) [Cu(Me6TREN)(Br)][Br].

of thermally induced side reactions. But, with a catalyst, a significant amount, if not all, of the substrate was converted into monoadducts. This supports what they learned in general chemistry courses, that catalysts lower the activation energy barrier for reactants by providing an alternate reaction pathway. For instructors, this component of the experiment provides some versatility as students can be tasked with synthesizing any transition-metal complex published and then asked to test its efficiency as a catalyst. Student groups could use the same ligand but incorporate different metals, or use the same metal and employ different ligands. This option, in addition to other reaction components that can be changed, provides instructors with an adaptable experiment that can be implemented in different ways for several years. Students tested four complexes varying both metal and ligands as shown in Figure 3. Reducing Agent. As detailed earlier, student groups used ascorbic acid in all of their ATRA reactions. Reaction Solvent. Due to the low solubility of ascorbic acid in most organic solvents, except for water and methanol,25 the solvent choice for all complex solutions and ATRA reactions was methanol. Internal Standard. 1H NMR spectroscopy was used to analyze the product of each reaction, and 1,4-dimethoxybenzene was used as the internal standard producing an unobstructed reference peak at 6.83 ppm integrated to a calibrated value of 1.000.

Table 1. ATRA of CBr4 to 1-Octene Using [Cu(TPMA)(Br)][Br] as Catalyst Monoadduct Yield,a % Alkene/Catalyst Ratio

Trial 1b

Trial 2b

Trial 3b

1-Octene

Blank 500/1 1,000/1 2,500/1 5,000/1 10,000/1 25,000/1

0.0 82.3 82.0 81.0 79.5 78.9 76.8

0.0 82.7 81.4 82.1 79.6 78.4 77.2

0.0 82.8 82.3 81.1 80.3 77.9 75.6

a

Yield (%) values for each sample were determined using integrations obtained from individual 1H NMR spectra (relative errors are ±10%).20 bATRA reactions were performed in methanol at 60 °C for 48 h with [alkene]/[alkyl halide]/[ascorbic acid] ratios set at [1.00]/ [1.10]/[0.05].

consistently obtained good and comparable yields for each trial, demonstrating the reliability of the reaction model. This experiment was important to perform, establishing that ATRA reactions could be repeated by different student groups with similar results. The 1H NMR spectra obtained for two trials are shown in Figure 4; complete 1H NMR spectra obtained for all trials are provided in the Supporting Information, pp S:11−S:13.

■

EXPERIMENT HAZARDS Standard laboratory precautions should be followed when handling all chemicals. Students should wear personal protective equipment including lab coats, gloves, and safety glasses. Reaction solvents are flammable and should be stored in appropriate storage cabinets. The ligand precursors formaldehyde, 2-pyridinecarboxaldehyde, tris(2-aminoethyl)amine, and 2-(aminomethyl)pyridine are acutely toxic and should be stored in a refrigerator. Olefins (1-hexene, 1-octene, 1-decene, styrene, and methyl acrylate) are flammable and should be stored in a refrigerator. Metal salts (CuBr2, NiBr2, and CoBr2) should be stored under ambient conditions. Sodium triacetoxyborohydride and sodium borohydride are hygroscopic and should be stored in a desiccator. All ligands and complexes made in this experiment are acutely toxic and can be harmful if ingested. Carbon tetrabromide (CBr4) and some NMR solvents are suspected carcinogens. NMR samples should be handled with care, prepared in a laboratory outside of the instrument room, and disposed of properly.

■

Alkene

Experiment 2: Varying Alkene Substrates

Students varied the alkene substrate to examine the ability for ATRA to functionalize different olefins. Using CBr4 as the alkyl halide and [Cu(TPMA)(Br)][Br] as catalyst, they tested 3 straight-chain alkenes (1-hexene, 1-octene, 1-decene), one aromatic alkene (styrene), and an organic ester (methyl acrylate). As presented in Table 2, they obtained very good yields for all straight-chain alkenes, except for 1-decene, which led them to conclude that the yield of addition decreased as the chain length grew. For styrene, they noticed thermally induced monoadduct formation in the blank sample, an outcome that is documented in the literature.21 Nonetheless, they saw a significant difference in yield when a catalyst was used at high loadings and appreciated the role of a catalyst in this reaction. They obtained good addition yields with the organic ester but only at high catalyst loadings. These experiments reinforced one distinctive characteristic of catalysts taught in general chemistry, which is that a small amount of catalyst should be able to “convert” a large amount of the substrate. In the straight-chain alkene experiment, students saw that, regardless of chain length, just 1 mol of the catalyst converted 5,000 mol of the substrate at very good yields and that, for 1-hexene, 1 mol of catalyst converted as much as 25,000 mol of the substrate at very good yields. 1H NMR spectra obtained for the styrene experiment are shown in Figure 5, and spectra from all ATRA experiments are provided in the Supporting Information, pp S:14−S:18.

RESULTS AND DISCUSSION

Experiment 1: Repeated ATRA Reaction

Students performed three trials of the same experiment testing the addition of CBr4 to 1-octene at 60 °C for 48 h using [Cu(TPMA)(Br)][Br] as a catalyst. As shown in Table 1, they C




Figure 4. 1H NMR spectra (400 MHz, CDCl3) for the ATRA of CBr4 to 1-octene using [Cu(TPMA)(Br)][Br] as catalyst: (I) trial 1 and (II) trial 3.

Table 2. ATRA of CBr4 to Different Alkene Substrates Using [Cu(TPMA)(Br)][Br] as Catalyst Monoadduct Yield,a % b

b

Alkene/Catalyst Ratio

1-Hexene

1-Octene

1-Deceneb

Styreneb

Methyl Acrylateb

Blank 500/1 1,000/1 2,500/1 5,000/1 10,000/1 25,000/1

0.0 93.9 91.8 87.7 83.8 80.6 77.5

0.0 82.8 82.3 81.1 80.3 77.9 75.6

0.0 78.2 77.3 75.3 73.3 53.4 31.1

25.5 63.9 61.7 57.0 52.9 42.3 29.3

0.0 88.3 83.0 77.2 46.4 1.5 0.0

Yield (%) values for each sample were determined using integrations obtained from individual 1H NMR spectra (relative errors are ±10%).20 ATRA reactions were performed in methanol at 60 °C for 48 h with [alkene]/[alkyl halide]/[ascorbic acid] ratios set at [1.00]/[1.10]/[0.05].

a

b

Experiment 3: Varying Catalyst Metal

sphere. On the other hand, the metal center in the nickel complex, [Ni(TPMA)(Br2)], adopted a distorted octahedral geometry with both bromide ligands coordinated to the metal (Figure 6C). The metals used provided a comparison within the same transition-metal row of the periodic table, with the only difference being metal group and number of electrons available in each metal’s d-orbital. Instructors can pick metals in different rows to explore the effect atom size may have on catalysis results as one way to modify this experiment. As shown in Table 3, students observed that the cobalt complex produced higher addition yields for both alkenes. Compared to the copper complex, the nickel complex produced higher yields for 1-octene at all catalyst loadings, but only three loadings in the 1-decene experiment (500/1; 1,000/1; 10,000/

To explore what effect that metal used in catalyst design had on ATRA, students performed experiments on the addition of CBr4 to 1-octene and 1-decene at 60 °C for 48 h using the ligand TPMA and three different metal bromide salts: CuBr2, CoBr2, and NiBr2. The bromide counterion was necessary to match the halide atom in the alkyl halide substrate (CBr4). Complexes were made and characterized using X-ray diffraction as disseminated in the preliminary synthesis experiment.19 The molecular structure obtained for the copper complex, [Cu(TPMA)(Br)][Br], was similar to that of the cobalt complex, [Co(TPMA)(Br)][Br], as shown in Figure 6A,B. Each metal center adopted a distorted trigonal bipyramidal geometry with the second bromide ligand located outside the coordination D




Figure 5. 1H NMR spectra (400 MHz, CDCl3) for the ATRA of CBr4 to styrene using [Cu(TPMA)(Br)][Br] catalyst after 48 h.

Figure 6. Molecular structures at 50% probability ellipsoids for (A) [Cu(TPMA)(Br)][Br], (B) [Co(TPMA)(Br)][Br], and (C) [Ni(TPMA)(Br2)].

ligand, TPMA. Copper(II) bromide complexes were made using each ligand and characterized using X-ray diffraction. Molecular structures obtained by students are shown in Figure 8. The Me6TREN complex displayed a similar distorted trigonal bipyramidal geometry when compared to the TPMA complex (Figure 8). As shown in Table 4, students observed that the Me6TREN complex produced lower addition yields for both 1octene and 1-decene, which may be due in part to steric hindrance from the methyl groups of the Me6TREN ligand. A set of comparison 1H NMR spectra for 1-octene are shown in Figure 9, with complete spectra provided in the Supporting Information document, pp S:23−S:24.

1). This prevented students from reaching the straightforward conclusion that their nickel complex was better than their copper complex. This was a welcomed outcome as students learned a valuable lesson most scientists encounter: Experiments incorporating different parameters do not always produce perfect outcomes. Thus, students need to learn how to develop the important skill of communicating these types of results during the developmental stage of their academic careers, and this experiment provided that. Nevertheless, their data continued to suggest that ATRA yields do decrease with increased chain length as reported by other student groups earlier. A set of comparison 1H NMR spectra obtained for the ATRA of CBr4 to 1-octene using the nickel and cobalt complexes are presented in Figure 7.

Experiment 5: Varying Reaction Temperature

To reinforce another concept students learned in general chemistry, that higher reaction temperatures usually lead to faster reaction kinetics producing higher yields, students investigated the ATRA of CBr4 to 1-octene using catalyst loadings of (500/1 and 5,000/1) for [Cu(TPMA)(Br)][Br] at four temperatures (25, 40, 50, and 60 °C). As shown in Table 5,

Experiment 4: Varying Catalyst Ligand

To investigate the effect of catalyst ligand on ATRA, students synthesized another tetradentate ligand incorporating aliphatic N-donor groups, tris(2-dimethylaminoethyl)amine) (Me6TREN), to compare to the initial aromatic N-donor E




°C, and a steady rise when it changed from 40 to 60 °C (Figure 10). Students did not perform ATRA experiments higher than 60 °C because the boiling point of methanol is 64.7 °C.

Table 3. ATRA of CBr4 to Alkenes Using [Cu(TPMA)(Br)][Br], [Ni(TPMA)(Br2)], and [Co(TPMA)(Br)][Br] as Catalyst

■

Monoadduct Yield,a % Alkene


Cub

Nib

Cob

1-Octene

Blank 500/1 1,000/1 2,500/1 5,000/1 10,000/1 Blank 500/1 1,000/1 2,500/1 5,000/1 10,000/1

0.0 82.8 82.3 81.1 80.3 77.9 0.0 78.2 77.3 75.3 73.3 53.4

0.0 88.7 86.4 85.4 83.1 80.2 0.0 81.0 79.2 68.4 61.9 57.6

0.0 94.1 91.6 89.8 87.5 85.8 0.0 87.3 85.0 82.5 70.0 66.7

1-Decene

ASSESSMENT AND OUTCOMES The pedagogical goals established for this experiment were achieved. (1) Students were able to apply the compounds made in a preliminary synthesis and characterization experiment as catalysts in ATRA, providing them with an opportunity to learn about the utility of their compounds. (2) They observed the useful role catalysts play in organic transformation reactions as ATRA reactions performed with catalysts produced high addition yields and those performed without catalysts produced little or no monoadduct yields. (3) Through formal reports and oral presentations, students were able to express an appreciation for the integrated nature of this experiment.

a

Yield (%) values for each sample were determined using integrations obtained from individual 1H NMR spectra (relative errors are ±10%).20 bATRA reactions were performed in methanol at 60 °C for 48 h with [alkene]/[alkyl halide]/[ascorbic acid] ratios set at [1.00]/ [1.10]/[0.05].

They learned to survey the literature to find synthesis and catalysis procedures. They used organic chemistry concepts to synthesize their ligands, inorganic chemistry concepts to synthesize their complexes, analytical chemistry to characterize their compounds, and organometallic chemistry to execute and analyze their catalysis experiments. The learning objectives

they observed that increasing the reaction temperature does produce higher addition yields. They saw a significant jump in monoadduct yield when the temperature changed from 25 to 40

Figure 7. 1H NMR spectra (400 MHz, CDCl3) for the ATRA of CBr4 to 1-octene using (I) [Co(TPMA)(Br)][Br] and (II) [Ni(TPMA)(Br2)] catalysts. F




Figure 8. Molecular structures shown at 50% probability ellipsoids obtained for (A) [Cu(TPMA)(Br)][Br] and (B) [Cu(Me6TREN)(Br)][Br].

Table 4. ATRA of CBr4 to Select Alkenes Using [Cu(TPMA)(Br)][Br] and [Cu(Me6TREN)(Br)][Br] as Catalyst Monoadduct Yield,a % Alkene


[Cu(TPMA)(Br)][Br]

[Cu(Me6TREN)(Br)][Br]b

1-Octene

Blank 500/1 1,000/1 5,000/1 10,000/1 Blank 500/1 1,000/1 5,000/1 10,000/1

0.0 82.8 82.3 80.3 77.9 0.0 78.2 77.3 73.3 53.4

0.0 80.3 72.5 64.5 56.6 0.0 70.4 66.8 60.3 52.2

1-Decene

b

Yield (%) values for each sample were determined using integrations obtained from individual 1H NMR spectra (relative errors are ±10%).20 ATRA reactions were performed in methanol at 60 °C for 48 h with [alkene]/[alkyl halide]/[ascorbic acid] ratios set at [1.00]/[1.10]/[0.05].

a

b

Figure 9. 1H NMR spectra (400 MHz, CDCl3) for the ATRA of CBr4 to 1-octene using (I) [Cu(TPMA)(Br)][Br] and (II) [Cu(Me6TREN)(Br)][Br].

1 Their ability to set up ATRA reactions with correct reagent amounts 2 Ability to obtain 1H NMR results from reactions

established for this experiment are also provided in the Supporting Information, p S:33. Students were assessed on these criteria: G




mole ratios, and reaction temperature. Issues encountered by students during this experiment were the following: • Forgetting to include a reagent when making stock solutions • Loss of stock solution due to evaporation from holding vials • Spillage when transferring stock solution into designated reaction tubes • Loss of reaction solution when tubes were not sealed correctly • Formation of polymers in two olefin substrates initially tested (acrylonitrile and vinyl acetate) • NMR instrument lock and shim errors for samples without enough chloroform-d

Table 5. ATRA of CBr4 to 1-Octene Using [Cu(TPMA)(Br)][Br] as Catalyst at Different Temperatures Alkene/Catalyst Ratio and Monoadduct Yield,b % Alkene

Temperature,a °C

500/1

5000/1

1-Octene

25 40 50 60

19.9 56.0 67.4 86.6

11.1 51.2 63.8 75.0

ATRA reactions were performed in methanol at 60 °C for 48 h with [alkene]/[alkyl halide]/[ascorbic acid] ratios set at [1.00]/[1.10]/ [0.05]. bYield (%) values for each sample were determined using integrations obtained from individual 1H NMR spectra (relative errors are ±10%).20 a

■

3 Individual laboratory notebook checks

ASSOCIATED CONTENT

S Supporting Information *

4 Ability to individually communicate procedures, results, and conclusions in a formal laboratory report and oral presentation

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.8b00721. Experimental procedures, 1H NMR spectra for all reactions, and instructor’s notes (PDF, DOCX) Crystallographic information files for [Ni(TPMA)(Br2)], [Cu(TPMA)(Br)][Br], [Cu(Me6TREN)(Br)][Br], and [Co(TPMA)(Br)][Br] (ZIP)

During an exit survey, students expressed that this experiment helped them achieve each learning objective and provided them with a fulfilling experience (see the Supporting Information, p S:36).

■

■

CONCLUSION A laboratory experiment highlighting the important role of transition-metal catalysts in ATRA has been presented for use in the undergraduate curriculum. It is designed for students who have taken, or will be taking, an organic chemistry lecture course and provides instructors with a laboratory exercise that can be paired with lectures on addition reactions. It is a versatile module as instructors can vary different components of the experiment such as the reducing agent, catalyst metal, catalyst ligand, reaction solvent, alkene substrate, alkyl halide substrate, reagent

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Kayode D. Oshin: 0000-0002-4362-4337 Matthias Zeller: 0000-0002-3305-852X Notes

The authors declare no competing financial interest.

Figure 10. 1H NMR (400 MHz, CDCl3) for the ATRA of CBr4 to 1-octene using [Cu(TPMA)(Br)][Br] catalyst loadings of (I) 500/1 and (II) 5,000/ 1. H



■


(19) Bazley, I. J.; Erie, A. A.; Feiereisel, G. M.; LeWarne, C. J.; Peterson, J. M.; Sandquist, K. L.; Oshin, K. D.; Zeller, M. X-ray Crystallography Analysis of Complexes Synthesized with Tris(2pyridylmethyl)amine: A Laboratory Experiment for Undergraduate Students Integrating Interdisciplinary Concepts and Techniques. J. Chem. Educ. 2018, 95 (5), 876−881. (20) Taylor, M. J.; Eckenhoff, W. T.; Pintauer, T. Copper-Catalyzed Atom Transfer Radical Addition (ATRA) and Cyclization (ATRC) Reactions in the Presence of Environmentally Benign Ascorbic Acid as a Reducing Agent. Dalton Trans. 2010, 39 (47), 11475−11482. (21) Eckenhoff, W. T.; Pintauer, T. Copper Catalyzed Atom Transfer Radical Addition (ATRA) and Cyclization (ATRC) Reactions in the Presence of Reducing Agents. Catal. Rev.: Sci. Eng. 2010, 52 (1), 1−59. (22) Woodruff, S. R.; Davis, B. J.; Tsarevsky, N. V. Epoxides as Reducing Agents for Low-Catalyst-Concentration Atom Transfer Radical Polymerization. Macromol. Rapid Commun. 2014, 35 (2), 186−192. (23) Sigma Aldrich. Organic Building Blocks: Alkenes. https://www. sigmaaldrich.com/chemistry/chemistry-products.html?TablePage= 16274428 (accessed Apr 2019). (24) Tang, W.; Matyjaszewski, K. Effects of Initiator Structure on Activation Rate Constants in ATRP. Macromolecules 2007, 40 (6), 1858−1863. (25) Shalmashi, A.; Eliassi, A. Solubility of l-(+)-Ascorbic Acid in Water, Ethanol, Methanol, Propan-2-ol, Acetone, Acetonitrile, Ethyl Acetate, and Tetrahydrofuran. J. Chem. Eng. Data 2008, 53 (6), 1332− 1334.

ACKNOWLEDGMENTS The corresponding author would like to thank Creighton University and Purdue University for instrument support. This work was also supported by the National Science Foundation Major Research Instrumentation Program under Grant CHE1625543.

■

REFERENCES

(1) Belford, R. E.; Bastin, L. D. ConfChem Conference on Educating the Next Generation: Green and Sustainable ChemistryAn Online Conference. J. Chem. Educ. 2013, 90 (4), 508−509. (2) Haack, J. A.; Hutchison, J. E. Green Chemistry Education: 25 Years of Progress and 25 Years Ahead. ACS Sustainable Chem. Eng. 2016, 4 (11), 5889−5896. (3) Dicks, A. P.; Batey, R. A. Greening the Organic Curriculum: Development of an Undergraduate Catalytic Chemistry Course. J. Chem. Educ. 2013, 90 (4), 519−520. (4) Goldman, A. S. Organometallic chemistry: Carbon−Carbon Bonds Get Break. Nature 2010, 463 (11), 435−436. (5) Eckenhoff, W. T.; Pintauer, T. Structural Comparison of Copper(I) and Copper(II) Complexes with Tris(2-pyridylmethyl)amine Ligand in Atom Transfer Radical Addition. Inorg. Chem. 2010, 49 (22), 10617−10626. (6) Eckenhoff, W. T.; Garrity, S. T.; Pintauer, T. Highly Efficient Copper-Mediated Atom Transfer Radical Addition (ATRA) in the Presence of Reducing Agent. Eur. J. Inorg. Chem. 2008, 2008, 563−571. (7) Kharasch, M. S.; Urry, W. H.; Jensen, E. V. Addition of Derivatives of Chlorinated Acetic Acids to Olefins. J. Am. Chem. Soc. 1945, 67 (9), 1626−1626. (8) Kleij, A. W.; Gossage, R. A.; Jastrzebski, J. T.; Boersma, J.; van Koten, G. The “Dendritic Effect” in Homogeneous Catalysis with Carbosilane-Supported Arylnickel(II) Catalysts: Observation of Active-Site Proximity Effects in Atom-Transfer Radical Addition. Angew. Chem., Int. Ed. 2000, 39 (1), 176−178. (9) Severin, K. Ruthenium Catalysts for the Kharasch Reaction. Curr. Org. Chem. 2006, 10 (2), 217−224. (10) Eckenhoff, W. T.; Biernesser, A. B.; Pintauer, T. Structural Characterization and Investigation of Iron(III) Complexes with Nitrogen and Phosphorus-Based Ligands in Atom Transfer Radical Addition (ATRA). Inorg. Chim. Acta 2012, 382, 84−95. (11) Eckenhoff, W. T.; Pintauer, T. Atom Transfer Radical Addition in the Presence of Catalytic Amounts of Copper(I/II) Complexes with Tris(2-pyridylmethyl)amine. Inorg. Chem. 2007, 46 (15), 5844−5846. (12) Matyjaszewski, K. Atom Transfer Radical Polymerization (ATRP): Current Status and Future Perspectives. Macromolecules 2012, 45 (10), 4015−4039. (13) Matyjaszewski, K.; Tsarevsky, N. V. Macromolecular Engineering by Atom Transfer Radical Polymerization. J. Am. Chem. Soc. 2014, 136 (18), 6513−6533. (14) Clark, A. J. Copper Catalyzed Atom Transfer Radical Cyclization Reactions. Eur. J. Org. Chem. 2016, 2016, 2231−2243. (15) Shen, Y.; Cornella, J.; Julia-Hernandez, F.; Martin, R. VisibleLight-Promoted Atom Transfer Radical Cyclization of Unactivated Alkyl Iodides. ACS Catal. 2017, 7 (1), 409−412. (16) Beers, K. L.; Matyjaszewski, K.; Woodworth, B. Controlled/ Living Radical Polymerization in the Undergraduate Laboratories. 1. Using ATRP To Prepare Block and Statistical Copolymers of n-Butyl Acrylate and Styrene. J. Chem. Educ. 2001, 78 (4), 544−547. (17) Matyjaszewski, K.; Beers, K. L.; Metzner, Z.; Woodworth, B. Controlled/Living Radical Polymerization in the Undergraduate Laboratories. 2. Using ATRP in Limited Amounts of Air To Prepare Block and Statistical Copolymers of n-Butyl Acrylate and Styrene. J. Chem. Educ. 2001, 78 (4), 547−550. (18) Tsarevsky, N. V.; Woodruff, S. R.; Wisian-Neilson, P. J. An Undergraduate Chemistry Laboratory: Synthesis of Well-Defined Polymers by Low-Catalyst-Concentration ATRP and Postpolymerization Modification to Fluorescent Materials. J. Chem. Educ. 2016, 93 (8), 1452−1459. I


Using Transition-Metal Complexes as Catalysts for Radical Addition

Recommend Documents